Our Experience With the Short-Term EEG for Diagnosis of Epilepsy

Posted: August 17, 2011 in Epilepsy, Tourette Syndrome
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This is a follow-up to my blog called Enduring the first long-term EEG . . .   Read on if you want to know what life is like when your child is first diagnosed with epilepsy.  In my previous post I described my son’s first long-term video EEG and some of the frustrations we faced.

From 2002 until 2005 my son had  six short-term EEG’s and seven or eight long-term video EEG’s at four different clinics/hospitals, which included two of the leading clinics in the nation. We have done so many of them that I have lost count.  When my son first had seizures I was totally ignorant about the tests and how it was all done.  The following is a description of what happens for a short-term EEG.  We have had lots of experience with this and I thought it would be a good idea to share some of it for those that are just beginning their investigation of seizures.

Based on our experience the procedure for putting on the electrodes for an EEG are pretty consistent from clinic to clinic. In the first step the technician measures the patient’s head to correctly position each  electrode.  In the earlier days, they put marks on the head using what looked like a blue grease pencil. The pencil hurt and my son hated it. After about three years, at another clinic they actually used an EEG cap that had all of the electrodes on it and it was just a matter of getting it positioned correctly. More recently the clinics got smart and started using washable markers.  What a difference this made for my son.

The electrodes are placed on the head based on the  international 10–20 system which ensures that the naming of electrodes is consistent across laboratories.  For each electrode the EEG technician  does the following steps:

    • scrub the area with an abrasive soap to get rid of any dead skin cells.  Dead skin cells can diminish the effectiveness of the electrode.  The technician does this scrubbing using a Q-tip except the stick is wooden.  This was another aspect of the EEG that my son hated, because he said it hurt.
    • fill an electrode with a conductive pink gel or paste.  Each electrode consists of a small, tin cup which is connected to the wires.  The conductive gel is scooped into the cup of the electrode.
    • place the cupped portion of the electrode onto the marking on the head
    • soak a small swatch of gauze in glue.  The glue was another trigger for my son to become anxious and at times became hysterical.  It got to the point that all the technician had to do was bring out the brown bottle and my son would cry.
    • place the glue-soak gauze over the top of the electrode cup and onto the head.  The purpose of this is to keep the electrode in place.
    • connect the end of the electrode wire to an apparatus that tells the technician if they are getting a good reading.  The goal is to make all of the lights red.  If the reading is not good, the technician will use an instrument that looks like a hypodermic needle (which isn’t) to squirt more of the conductive gel under the electrode cup.  This instrument is also another aspect of the EEG that may make a child anxious.  It is not that it hurt; it is just that it looks like a shot needle and they are scared.

This whole process is started all over with the next electrode.  As you can see this is a laborious task and takes some time.  In most clinics there are 19 recording electrodes used, plus a ground and a system reference placed behind the ear and on the chest.  On a good day this process takes 40 minutes to one hour.  Now add to it the time it takes to get your child to calm down and endure the process.  This isn’t easy because they need to sit perfectly still.  Typically my son wanted to get up and run away.  After our first EEG we knew to bring in toys or food to distract him while the electrodes were put on.

With a short-term EEG the patient remains in a room on a bed.  The technician then goes through the steps of the EEG. The goal is to induce normal and abnormal EEG activity.  It isn’t always necessary to trigger an actual seizure because sometimes the EEG will show patterns that denotes  a seizure.  The technician guides the patient through a few tests while the EEG is capturing the brain activity.  These procedures were consistent for every clinic that we went to.  These tests include:

    • asking some simple questions for a response
    • opening and closing the eyes
    • hyperventilating by blowing on a pin wheel for about five minutes.  Over all of my son’s EEG’s he was never able to do this for five minutes.  This is one test that I had to really coax him to do it and keep doing it.
    • looking at a strobe light which is set to different frequencies
    • sleeping for a half hour.  This is also somewhat tricky.  Several of the clinics we went to did the tests early in the morning and had the parent get the child up in the night so that they are sleep deprived.  Sleep deprivation in some cases can trigger a seizure.  In addition this procedures helps your child fall asleep during that portion of the test.

Once all of brain activity is captured via the EEG, the technician helps take off all of the electrodes.  They use a special solvent that takes off most of the glue and electrodes.  Afterwards they wash the hair and scalp in an attempt to get all of the glue and gook off.  The first time my son had an EEG using glue his hair was long.  He has tight, curly hair and it was a nightmare trying to get all of the glue out.  Luckily he is a boy and we learned to cut his hair short which made it easy to get everything off.  One technician remarked that short hair is not necessarily the best, because the shortness of the hair can push against the electrode and reduce the effectiveness of the test.

That’s the end of the test and at this point all you have to do is wait.  Typically you have to wait for the results. There are a couple of things to keep in mind.

  • An EEG measures the brain waves on the surface of the brain.  If there are issues deeper than that they may not be detected on the EEG.
  • An EEG is not conclusive because there are so many factors that can influence it
  • The capture of the brain waves may be affected by “noise” during the EEG.  Noise is defined as other brain activity that may interfere with the results of the EEG.  Types of “noise” include:
    • Eye-induced artifacts (includes eye blinks, eye movements and extra-ocular muscle activity)
    • ECG (cardiac) artifacts
    • EMG (muscle activation)
    • Glossokinetic artifacts (tongue)

Recently, independent component analysis techniques have been used to correct or remove EEG contaminates.  These techniques attempt to “unmix” the EEG signals into some number of underlying components.

These artifacts were one of the major problems we had in diagnosing my son.  It took almost five years to confidently diagnose his seizures.  The reason it was so hard is because most of his daily seizures were facial oriented, with most activity associated with his eyes.  His seizures began with a tug at the right eye and then eye blinking, or eye fluttering, and sometimes head and body jerks.  Since these were eye focused it was difficult to differentiate the seizure movements from normal blinking movement.

In the beginning there was a lot of debate about what these events were.  My son’s videos of his events were looked at from doctors all over the country.  They were also reviewed at a symposium for practitioners who specialized in movements disorders, including tics.  The reviews also ended inconclusive.

The other factor to consider is whether your neurologist is a specialist in epilepsy and ideally an epitologist who is a neurologist that has specific training for diagnosing and treating epilepsy.  In our case it was an epitologist who was able to review the EEG results and eliminate the “noise” artifacts.  She also saw in some of the videos that my son struck a “fencing” position which is a particular type of movement with epilepsy.

It was Mayo Clinic that did a test that measures the speed the eye blinking during my son’s seizures.  Typically tics are mimicable and would have a speed that was equal to a normal eye blink.  The test showed that these blinks were considerably faster than a normal blink, which is what I had been saying for years.

The other thing to keep in mind is that there may be more than one thing going on at the same time.  This is the case with my son.  We have determined that he has movements that are a part of his epilepsy, movements that are associated with non-epileptic seizures, and movements associated with Tourette Syndrome.  It is interesting that earlier in our investigation tics were considered, and it is highly possible that he was having both seizures and tics.

Probably the best advice I can give you is follow your instincts.  When we were struggling to figure out what was going on with my son, I did a lot of research.  In those days the internet was not that prominent, both from quality of content and for user-friendly interfaces.  Instead I bought thousands of dollars of books, including text books.  I studied topics including epilepsy, movement disorders, non-epileptic seizures, myoclonic seizures and much more.  All during this time, my instinct told me that my son was having seizures.  I taught myself everything I could about the brain and neurological disorders.  I kept talking to doctors, learning more and more as I continued my research.

Persistence has paid off.  The neurologist determined that the source of my son’s seizures was the left frontal part of the brain and his latest seizures are classified as myoclonic seizures.  Between having a vagal nerve stimulator (VNS) and anti-epileptic drugs the majority of my son’s epileptic seizures are gone.  Rather than happening twenty times a day, he may have one seizure every other week or so.

I hope this post was helpful.  In the near future I will be writing a post about long-term video EEG.  Come back to my blog for more stories about the medical challenges my family have face.

To Be Continued . . .

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